This invention relates in general to a variable speed transmission device which provides a mechanical or positive connection between its drive and driven shafts. The transmission device of the present invention is capable of producing within a finite range of gear ratios an infinite number of gear ratios.
Many different types of transmission devices are presently available. All of these prior art devices, however, have a number of inherent disadvantages which significantly limit their use and effectiveness.
A transmission device is quite simply an apparatus for providing one or more different gear or drive ratios between its input and output shafts. In particular, a transmission device is typically operable to either increase the speed of its output shaft relative to the speed of its input shaft or vice versa. Heretofore, these speed changes have been effectuated by means of transmission devices comprising either gear trains or friction drives.
A gear train is normally comprised of a plurality of gears which are arranged to interact in order to transmit motion from an input shaft to an output shaft. The ratio between the speed of the input shaft and the speed of the output shaft is determined by the number of gears in the train, the number of teeth on each gear and the arrangement of the gears with respect to each other. In this type of transmission device, the gears in the train physically engage each other to provide a physical or positive connection between the input and output shafts. A physical or positive connection between the input and output shafts is highly desirable because it prevents the gear train from slipping during high power applications. Gear trains, however, are extremely limited in use because they are capable of producing only a single gear ratio between their input and output shafts. Accordingly, gear trains are not very versatile and can only be used in limited applications.
To overcome this disadvantage, many transmission devices are comprised of several gear trains and means for switching between the various gear trains to thereby provide a larger number of gear or drive ratios between the device's input and output shafts. The number of different gear ratios capable of being produced by such a transmission device, however, is still rather limited making it impossible to control the output speed of the output shaft within very small limits. Another disadvantage associated with transmision devices having changeable gear trains is that the device is normally of a fairly complex mechanical design. In particular, the device must be equipped with a clutch mechanism for disengaging the device from its corresponding source of power when the gear train is being changed. Such a device must also be equipped with mechanical means for changing from one gear train to another. Accordingly, transmission devices having changeable gear trains are complex in design, expensive to build and costly to maintain.
A friction drive, on the other hand, is typically comprised of a circular driving disc having its contacting face covered with a suitable friction material such as rubber, leather or brake lining and a driven wheel having a suitable material attached to its outer edge. The driving disc and driven wheel are normally positioned perpendicular to each other such that the outer edge of the driven wheel is in contact with the face of the driving disc. In this position, the rotational motion of the driving disc is imparted to the driven wheel with the rotating speed of the driven wheel being controlled by the position of the wheel relative to the center axis of the driving disc. As the driven wheel is moved along the radius of the driving disc, it's speed of rotation varies with position. When the distance from the center axis of the driving disc to the point of contact between the driven wheel and the face of the driving disc is equal to the radius of the driven wheel, the gear ratio between the input and output shafts is 1:1. As the driven wheel is moved closer to the center axis of the driving disc, the gear ratio is correspondingly reduced. The gear ratio, however, increases as the driven wheel is moved away from the center axis of the driving disc. As a result, this type of transmission device is capable of providing within set limits an infinite number of stepless ratio changes which allow the output speed of the output shaft to be controlled within very small limits.
While a friction drive is capable of producing a large range of ratio changes, the usefulness of this device is severely limited because it does not provide a physical or positive connection between its input and output shafts. In other words, the motion of the input shaft is transferred to the output shaft by means of the frictional contact between the driving disc and the driven wheel. Accordingly, this type of transmission device is not suitable for use in large power applications because of the power losses and wear that accompany slippage.
The transmission device of the present invention, however, exhibits the desirable features of both of these prior art transmission devices. In particular, the transmission device of the present invention is capable of producing within a finite range of gear ratios an infinite number of ratio changes to thereby control the speed of the output shaft within small limits, as can the prior art transmission devices comprised of friction drives. In addition, this transmission device provides a positive or mechanical connection between its input and output shafts to thereby make this device acceptable for use in large power applications, as are the presently known transmission devices utilizing gear trains. Accordingly, the transmission device of the present invention incorporates the desirable features of both of the prior art transmission devices.
The transmission device of the present invention is comprised of a pair of circular wheels having different diameters. In the preferred embodiment of the invention, the larger wheel is designated the drive wheel and has a plurality of movement imparting bars mounted on its drive face in a generally radial configuration. The other wheel is designated the driven wheel and is equipped with a plurality of cylindrically shaped movement receiving pegs which are mounted to this wheel such that a portion of each peg protrudes outward from the drive face of the wheel. These two wheels are positioned adjacent to each other such that the movement receiving pegs of the driven wheel are capable of physically engaging the movement imparting bars of the drive wheel. In this way, the movement imparting bars and movement receiving pegs interact to transmit rotational motion from the drive wheel to the driven wheel, with the speed of the driven wheel being determined by the position of the driven wheel relative to the drive wheel. By varying the relative position of these two wheels, the gear ratio between the device's input and output shafts is correspondingly changed to thereby provide within set limits an infinite range of stepless ratio changes which allow the output speed of the output shaft to be controlled within very small limits. Since the motion of the drive wheel is imparted to the driven wheel through the physical contact between the movement imparting bars on the drive wheel and the movement receiving pegs on the driven wheel, this device provides a physical or positive connection between its input and output shafts thereby making it suitable for use in connection with large power loads.
It is therefore an object of the present invention to provide a variable-speed transmission device which provides a mechanical or positive connection between its input and output shafts.
Another object of the present invention is to provide a variable-speed transmission device which is capable of producing within a finite range of gear ratios an infinite number of different gear ratios to thereby allow the output speed of the output shaft to be controlled within very small limits.
A further object of the present invention is to provide a variable-speed transmission device of the character described which is capable of changing the gear ratio between its input and output shafts while the device is operating under a load.
An additional object of the present invention is to provide a variable-speed transmission device of the character described which is capable of being used in connection with large power loads.
It is a further object of the present invention to provide a variable-speed transmission device of the character described which is simple to operate.
It is a further object of the present invention to provide a variable-speed transmission device of the character described which is simple and economical to construct and is reliable in operation.
Other and further objects of the invention together with the features of novelty and apurtenant thereto, will appear in the course of the following description.